March 11, 2014

Protostars In Orion Nebula Doomed By Larger Stars

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) found that some protostars in the Orion Nebula are doomed from the beginning.

The Orion Nebula has hundreds of young stars, or protostars, and even some “proplyds,” which are stars that are even younger than protostars. Astronomers have discovered that some of these young stars will have their planet-forming dust and gas blasted away from another star when they are only about 600 billion miles away.

"O-type stars, which are really monsters compared to our Sun, emit tremendous amounts of ultraviolet radiation and this can play havoc during the development of young planetary systems," Rita Mann, an astronomer with the National Research Council of Canada in Victoria, and lead author on a paper published in the Astrophysical Journal, said in a statement. "Using ALMA, we looked at dozens of embryonic stars with planet-forming potential and, for the first time, found clear indications where protoplanetary disks simply vanished under the intense glow of a neighboring massive star."

Many stars are born in crowded stellar nurseries similar to the Orion Nebula, and over the course of a few million years they collect grains of dust and gas. As these elements gather, they combine to form larger, denser bodies and could eventually help the systems evolve into fully-fledged star systems with planets.

Massive stars that live in and around large interstellar clouds are essential for the star growing process. When a massive star explodes into a supernova, it helps to refuel the area with dust and heavy elements.

However, the new survey discovered that these explosions do not always help replenish young stars, but sometimes actually strip away the planet building materials.

"Massive stars are hot and hundreds of times more luminous than our Sun," James Di Francesco, also with the National Research Council of Canada, said in a statement. "Their energetic photons can quickly deplete a nearby protoplanetary disk by heating up its gas, breaking it up, and sweeping it away."

Early Hubble Space Telescope observations have revealed that many proplyds in Orion had taken on tear-drop shapes, with their dust and gas trailing away from a nearby massive star. These images couldn’t reveal anything about the amount of dust that was present or how the dust and gas concentrations changed in relation to massive stars.

The ALMA observations detected these and other never-before-imaged proplyds, doubling the number of protoplanetary disks discovered in that region. ALMA allowed astronomers to look past the surface appearance of the young stars and measure how much mass was in the proplyds.

"Taken together, our investigations with ALMA suggest that extreme UV regions are not just inhospitable, but they’re downright hazardous for planet formation. With enough distance, however, it’s possible to find a much more congenial environment," said Mann. "This work is really the tip of the iceberg of what will come out of ALMA; we hope to eventually learn how common solar systems like our own are."